Various touch screens are used in a variety of electronic products, such as mobile phones, tablet computers, music players, etc. As a graphical user interface device, the touch screens include resistive type, capacitive type, surface acoustic wave type, infrared type and other types. Among different touch screen technologies, the capacitive touch screen has the advantages of a longer lifetime, higher transmissivity, a multi-point touch support, etc., as compared with the resistive touch screen. Mutual capacitance touch sensing is emerging as a technology for the capacitive touch screen, and has good suppression of noise and of parasitic capacitance to ground, and can provide a multi-point touch surface. Thus, the mutual capacitance touch sensing device is becoming a main thrust for various manufacturers of capacitive touch screen chips.
FIG. 1 illustrates a schematic sectional structural view of a liquid crystal display panel of an existing in-cell mutual capacitance touch screen. Refer to FIG. 1, the liquid crystal display panel includes an array substrate 11 and a color filter substrate 13 which are opposed each other. The array substrate 11 includes an array of Thin Film Transistors (TFTs) and an array of pixel electrodes. The liquid crystal display panel further includes a liquid crystal layer 12 disposed between the array substrate 11 and the color filter substrate 13; a touch sense electrode structure 14 formed on the color filter substrate 13. The touch sense electrode structure 14 includes a matrix structure formed of a plurality of drive electrodes and a plurality of sense electrodes which intersect each other, and mutual capacitances are formed between the drive electrodes and the sense electrodes. The liquid crystal display panel also includes a black matrix 15 formed on the touch sense electrode structure 14. Moreover, different types of crystal liquid display panels are somewhat different in structure, for example, for an In-Plane-Switching (IPS)-type liquid crystal panel or a Fringe Field Switching (FFS)-type liquid crystal panel, common electrodes are disposed in the layer 11 of the array of TFTs and the array of pixel electrodes; and for a Twisted Nematic (TN)-type liquid crystal panel or a Vertical Alignment (VA)-type liquid crystal panel, common electrodes are a part of the color filter substrate 13. In a practical application, a glass substrate (not illustrated in FIG. 1) is formed respectively on the outside of the layer 11 of the array of TFTs and the array of pixel electrodes and of the black matrix 15. In a conventional in-cell mutual capacitance touch screen, in order to lower parasitic capacitances between the drive electrodes or sense electrodes and the other electrodes in the liquid crystal panel, the area of the drive electrodes and the sense electrodes is reduced as much as possible, therefore, a blank area is left in the touch sense electrode structure 14 other than the drive electrodes and the sense electrodes, thus resulting in a non-uniform transmissivity distribution across the liquid crystal display panel and degrading the display performance.
Moreover since the drive electrodes and the sense electrodes in the in-cell mutual capacitance touch screen are at a very short distance from the other electrodes, e.g., pixel electrodes, common electrodes, etc., of the liquid crystal display than the drive electrodes and the sense electrodes, there are parasitic capacitances between the drive electrodes in the in-cell mutual capacitance touch screen and the other electrodes (e.g., the common electrodes), and between the sense electrodes in the in-cell mutual capacitance touch screen and the other electrodes (e.g., the common electrodes).
FIG. 2 illustrates a schematic diagram of an equivalent circuit of the in-cell mutual capacitance touch screen. Referring to FIG. 2, the equivalent circuit includes a signal source 141, a drive electrode resistance 142, a mutual capacitance 143 between a drive electrode and a sense electrode, a sense electrode resistance 144 and a detection circuit 145. There is a parasitic capacitance Cd between the drive electrode and a common electrode, and there is a parasitic capacitance Cs between the sense electrode and the common electrode, and thus noise is introduced to the liquid crystal display panel. This noise is generally generated by: 1) a part of signal current input by a drive line is bypassed by Cd, and the other part thereof is coupled to a signal receiver through Cs, and capacitance values of Cd and Cs change frequently due to overturn of liquid crystal molecules in a liquid crystal layer, so does a coupled signal, and thereby generating noise; 2) the common electrode is typically of the indium tin oxide (ITO) material which has a large resistance, and inherent noise on the common electrode is coupled directly to the signal receiver through Cs. The presence of noise affects the detection of a sense signal of the touch screen, that is, the liquid crystal display panel cannot detect accurately a touch by a finger of a user and consequently cannot respond to the touch by the finger in a timely manner.